Spark ignition internal combustion engines generally comprise one or more cylinders which act to compress a fuel-air mixture. The compressed mixture is ignited at a selected instant by a spark plug to drive the piston to provide energy. The timing of the spark is crucial to engine performance, affecting both work output and engine emissions.
Spark plugs are conventionally grounded to the engine body and electrically coupled to a distribution wire which delivers a high-voltage signal to produce the spark. Timing is controlled by an external distributor. The high voltage required by conventional spark plugs can interfere with radio reception and represent a hazard to repair personnel.
Because of these problems, it has been proposed in U.S. Pat. No. 4,412,151 to Norris to create a spark plug which is receptive to a low voltage signal. The low voltage signal activates a device such as a striker which impacts a piezoelectric element. The piezoelectric element develops a high voltage as a result of the impact and generates a spark to ignite the fuel-air mix.
While the spark plug of Norris allows the elimination of high-voltage wires from most accessible parts of the engine, it is still subject to timing difficulties. Further, fatigue becomes a significant consideration when a striker apparatus is used in a device which must endure for thousands of hours at speeds of 50 cycles per second or more. Minimization of the number of moving parts is desirable for any improved type of plug.
A need therefore exists for a spark plug which can automatically control cylinder timing in response to cylinder pressure, and which eliminates the need for external high-voltage wires. Ideally, such a spark plug would be compatible with existing engines, and would have a lifetime similar to or longer than a conventional spark plug. There also exists a need for a spark plug capable of providing information relevant to combustion efficiency and proper engine timing.